Method and apparatus for producing zeolite

ABSTRACT

A composition comprising an incineration ash or an aluminosilicate as a raw material is added with an aqueous alkaline solution from an alkali storage tank ( 3 ) and heated. The resultant pre-mixture is then mixed and kneaded by a kneader ( 4 ) to prepare a kneaded mixture ( 19 ) in the form of a slurry or mud. The kneaded mixture ( 19 ) is moved continuously and irradiated directly with an electromagnetic wave of 300 MHz to 30 GHz in an electromagnetic wave irradiation unit ( 21 ), to thereby convert it to zeolite. The zeolite thus formed is cleaned by means of a cleaning machine ( 7 ) and dried with a rotary steam dryer ( 9 ). This method can be employed for producing an artificial zeolite with a reduced amount of alkali used and discharged, at a lower energy expenditure, and a reduced time for production.

TECHNICAL FIELD

[0001] The present invention relates to a technology for producingzeolite from incineration ash or a composition containingaluminosilicate as a raw material.

BACKGROUND ART

[0002] Conventionally, fly ash generated in the course of coal burningand a composition containing aluminosilicate have been used as rawmaterials for producing artificial zeolite. Japanese Unexamined PatentPublication No. 6-321525 and No. 6-321526 disclose methods andapparatuses for producing zeolite from such raw materials by means of ahot aqueous alkaline solution.

[0003] Japanese Unexamined Patent Publication No. 10-324518 discloses amethod of continuously producing artificial zeolite by a circulatingfluidized-bed as well as a device therefor.

[0004] In the conventional methods of producing artificial zeolite, amixture formed by mixing fly ash or a composition containingaluminosilicate with an alkali is heated by radiation heat or conductionheat. The thermal energy density has limits to increase, which oftenmakes a heating time longer. Further, the reaction speed of formingzeolite with a hot aqueous alkaline solution is slow, thereby taking alonger time to produce artificial zeolite. In other words, heating isperformed from outside of particles, and therefore a longer time isneeded for heat influx into the particles and for diffusion of analkali, resulting in a longer reaction time as a whole.

[0005] In addition, the zeolite generated by the thermal alkalinereaction forms crust over the particle surface, retarding the reactioninside the particles. Thus, the formation of zeolite is hindered, andthe zeolite conversion rate is not high.

[0006] Furthermore, in the conventional methods, a large amount ofsodium hydroxide which is not involved in the reaction requires a largeamount of work and time in recovering and reutilizing the alkali, makingit difficult to produce artificial zeolite having a high function at alow cost.

[0007] There is a further problem from a viewpoint of energy savingsince the conventional methods require the steps of separatingartificial zeolite from an alkaline solution, and washing and drying thezeolite, and the separating and drying steps need a large amount ofenergy, resulting in a high production cost.

[0008] An object of the present invention is to provide a technologywhich enables production of artificial zeolite by a simpler process,compared with the conventional technology, with a reduced amount ofalkali used and discharged at a lower energy expenditure, and a reducedtime for production.

DISCLOSURE OF INVENTION

[0009] In order to solve the above-described problems, the method forproducing zeolite according to the present invention comprises adding anaqueous alkaline solution to incineration ash or a compositioncontaining aluminosilicate to prepare a mixture in the form of slurry ormud, heating the mixture, and directly irradiating the mixture withelectromagnetic waves having frequencies ranging from 300 MHz to 30 GHz,while continuously moving the mixture, to form the zeolite. By employingthis process, an alkali in a minimum amount necessary for the reactionpenetrates into the particle solid phase of incineration ash or thelike, and the alkali instantly forms zeolite by means of the heatgenerated from inside the particles by the electromagnetic waveirradiation. This process, therefore, enables the production ofartificial zeolite in a short time, with a reduced amount of alkali usedand discharged. Further, the conventional solid-liquidseparation/purification processes are not necessary, thereby simplifyingthe whole process.

[0010] It is noted that incineration ash or a composition containingaluminosilicate may include natural zeolite and artificial zeoliteproduced by other production methods which have not been converted intophillipsite. Accordingly, the present invention can be applied toimproving the properties of natural or other zeolite.

[0011] Since the electromagnetic wave irradiation causes heat generationonly in the mixture of incineration ash or the like, virtually withoutheating the surrounding devices, the atmospheric gases, etc., the heatefficiency is high and the energy expenditure can be lowered.Furthermore, the electromagnetic wave is irradiated after the mixture isheated, thereby raising the heat conversion efficiency to approximately70%. As this preliminary heating process, the mixture is preferablyheated at a temperature ranging from 80 to 150° C.

[0012] The principal component of the zeolite produced according to thepresent invention is phillipsite. It may also include faujasite, zeoliteA, hydroxy sodalite, etc. with non-zeolite components, that is,components other than zeolites, such as unburned carbon, iron, etc.

[0013] It is noted that the incineration ash described in the presentinvention is incineration ash made of compositions containingaluminosilicate. The incineration ash includes coal ash, incinerationash of sludge generated in paper manufacturing, incineration ash fromactivated sludge produced by sewage disposal, incineration ash from citygarbage, incineration ash of solidified fuel made from garbage or thelike. The composition containing aluminosilicate refers to a mineralcontaining a salt formed by partially substituting silicate or silicondioxide with aluminum. Such mineral is exemplified as orthoclase,anorthite, analcime, chabazite and mica.

[0014] By irradiating the electromagnetic waves having frequenciesranging from 300 MHz to 30 GHz, the dipole moments of water moleculesexisting in the mixture of incineration ash or a composition containingaluminosilicate and an aqueous alkaline solution vibrate vigorously(from several hundred million to several billion times per second) togive a high temperature by generating heat inside the particles ofincineration ash or the like, which promotes a hot alkaline reactioninstantly. Thus, the reaction to form zeolite, which took several hoursto several tens of hours according to the conventional methods, can becompleted in several minutes.

[0015] Since the mixture of incineration ash or a composition containingaluminosilicate and an aqueous alkaline solution is in the form ofslurry or mud, the handling and transportation efficiency in theproduction process are improved. Further, an efficient heat generationcan be realized by the electromagnetic wave irradiation. Thus, theamount of alkali can be adjusted to a minimum necessary for thereaction, resulting in great reduction of the amount of discharged wastealkali.

[0016] The reaction to form zeolite nuclei which determines the rate ofoverall reaction to form zeolite is accelerated by adding particles fornucleus formation in advance to incineration ash or a compositioncontaining aluminosilicate. Thus, the reaction speed of forming, zeoliteis raised by three to five times, thereby producing artificial zeolitein a shorter time. As the particles for nucleus formation, zeoliteparticles, glass powder, etc. are suitable.

[0017] Since a mixture of incineration ash or a composition containingaluminosilicate and an aqueous alkaline solution is continuously movedduring irradiation of electromagnetic waves, the control and adjustmentof the irradiation conditions are easier, allowing continuous working ofthe overall process for producing zeolite. Accordingly, the efficiencyof the process is enhanced. It is noted that, if the mixture ofincineration ash or the like has edges or protrusions, the electricfield tends to concentrate on the edges or protrusions, causing unevenheating. It is preferable to employ a cylindrical rotary heater or aconveyor-type heater which can move the heating surface up and down toprevent such uneven heating.

[0018] By using, as incineration ash, fly ash formed in the course ofcoal burning or garbage incineration, industrial wastes can be convertedinto useful resources. Fly ash formed in the course of coal burningrefers to minute ash particles collected by a dust collector in thecourse of coal burning using a pulverized coal-fired boiler. The ashparticles include silicon oxide, aluminum oxide, calcium oxide, etc.,with an ignition loss of 5% or less and a specific gravity of 1.9 ormore, having a particle size distribution passing 75% or more of theparticles through a 44 μm standard sieve. Fly ash generated by garbageincineration has a composition containing silica, alumina and lime,which is similar to the fly ash generated by coal burning.

[0019] The apparatus for producing zeolite according to the presentinvention is an apparatus comprising: kneading means for adding anaqueous alkaline solution to incineration ash or a compositioncontaining aluminosilicate to form a mixture and for kneading themixture; heating means for heating the mixture kneaded by the kneadingmeans; electromagnetic wave irradiation means for irradiating the heatedmixture with electromagnetic waves to form zeolite; cleaning means forcleaning the zeolite formed by the electromagnetic wave irradiation; anddrying means for drying the cleaned zeolite.

[0020] The apparatus having the above construction realizes a simplerprocess for producing artificial zeolite, compared with the conventionaltechnology, with a reduced amount of alkali used and discharged, at alower energy expenditure, and a reduced time for production.

BRIEF DESCRIPTION OF DRAWINGS

[0021]FIG. 1 is a schematic view showing a process in an apparatus forproducing zeolite.

[0022]FIG. 2 is a side view showing an electromagnetic wave irradiationunit in the apparatus for producing zeolite shown in FIG. 1.

[0023]FIG. 3 is a schematic view showing an electromagnetic wavegenerator for the electromagnetic wave irradiation unit shown in FIG. 2.

BEST MODE FOR CARRYING OUT THE INVENTION

[0024] Following are explanations of an embodiment of the presentinvention referring to the drawings.

[0025] As shown in FIG. 1, incineration ash such as fly ash transportedby a transportation vehicle or the like is stored in a raw materialreceiving vessel 1 and then sent to a preliminary heater 2 by a conveyerpump. Then an aqueous alkali at an alkali concentration of 1 to 30percent by weight is added from an alkali storage tank 3. The mixture isheated to 80 to 150° C., and then sent into a kneader 4 here the mixtureis kneaded. The preliminary heater 2 is heated with steam 17, and thekneader 4 is operated by a motor 18.

[0026] A kneaded mixture 19 in the form of slurry formed in the kneader4 is placed on a conveyor 20 and conveyed to an electromagnetic waveirradiation unit 21. While the mixture is being conveyed, the mixture isirradiated with electromagnetic waves having a frequency of 2,450 MHzfrom electromagnetic wave irradiators 5 located over the conveyor 20 for1 to 15 minutes. In this way, the reaction for zeolite generationprogresses rapidly in the kneaded mixture 19, forming zeolite. It isnoted that the electromagnetic wave irradiation conditions can beadjusted in frequencies ranging from 300 MHz to 30 GHz (wavelength: 1cm−1 m) and in the irradiation time ranging from 1 to 30 minutes.

[0027] After completion of the electromagnetic wave irradiation, thekneaded mixture 19 is cured and then sent to a cleaning machine 7 wherealkali attached to the formed zeolite is washed off. Then, the cleanedzeolite is dehydrated by a centrifuge 8 and mildly dried with steamheating in a rotary steam dryer 9 to produce artificial zeolite. Theartificial zeolite is put into a product receiving vessel 10, weighed toa specific weight value, packed, and shipped out as a product 16.

[0028] The aqueous alkali generated from the centrifuge 8 is sent to analkali receiving tank 11, treated in a primary waste water treatmentapparatus 12 and a secondary waste water treatment apparatus 13, passesthrough a monitoring apparatus 14, and then discharged as waste water15.

[0029] In the electromagnetic wave irradiation unit 21, as shown in FIG.2, a feed adjuster 22 for the kneaded mixture 19 is located in theproximity of the start of the conveyor 20, and a plurality ofelectromagnetic wave irradiators 5 are disposed over the conveyor 20. Acuring floor 25 for the formed zeolite is located in the proximity ofthe end of the conveyor 20, and a microwave prevention guide 26 isdisposed inside the conveyor 20.

[0030] As shown in FIG. 3, adjacent to the microwave transmitter 23,disposed are an isolator 24 which prevents leak of the microwavesgenerated, a directional coupler 27 for transmitting the generatedmicrowaves to a microwave irradiation section 32, a power monitor 28, anindicator 29, a matching device 30, a fixed distributor 31, and themicrowave irradiation section 32 for irradiating a materiel to be heatedwith microwaves, etc.

[0031] In the kneaded mixture 19 sent through the feed adjuster 22 andplaced on the conveyor 20, reaction for zeolite generation rapidlyprogresses by irradiation with microwaves generated by the microwavetransmitter 23 while the kneaded mixture 19 is being conveyed and,therefore, zeolite is formed in a short time until the mixture reacheshe end of the conveyer 20. The zeolite thus formed is cured in thecuring floor 25, and then sent, as described above, to the cleaningmachine 7 in which a specific treatment is performed.

[0032] Accordingly, in the course of adding an aqueous alkaline solutionto incineration ash, kneading the resultant mixture, heating the kneadedmixture 19 thus formed, and irradiating the kneaded mixture 19 withelectromagnetic waves to form zeolite, a minimum amount of alkalinecessary for the reaction penetrates into the particle solid phase ofincineration ash, and the alkali instantly forms zeolite by means of theheat generated from inside the particles by the electromagnetic waveirradiation. This process, therefore, enables production of artificialzeolite in a short time, with a reduced amount of alkali used anddischarged. Further, the conventional solid-liquidseparation/purification processes are unnecessary, thereby simplifyingthe whole process.

[0033] Additionally, since the electromagnetic wave irradiation causesheat generation only in the kneaded mixture 19, virtually withoutheating the surrounding devices, the atmospheric gases, etc., the heatefficiency is high and the energy consumption can be lessened.Furthermore, the electromagnetic wave is irradiated after the kneadedmixture 19 is preliminarily heated to approximately 80 to 150° C. ,thereby raising the heat conversion efficiency to approximately 70%.

[0034] The principal component of the zeolite formed by the embodimentof the present invention is phillipsite. It may also include faujasite,zeolite A, hydroxy sodalite, etc. with non-zeolite components, that is,components other than zeolite, such as unburned carbon, iron, etc.

[0035] By irradiating the mixture with electromagnetic waves having afrequency of 2,450 MHz, the dipole moments of water molecules existingin the kneaded mixture 19 vibrate vigorously (from several hundredmillion to several billion times per second) to give a high temperatureby generating heat inside the particles of incineration ash or the like,which promotes a hot alkaline reaction instantly. Thus, the reaction toform zeolite, which took from several hours to several tens of hoursaccording to the conventional methods, can be completed in severalminutes.

[0036] Since the kneaded mixture 19 is in the form of slurry, thehandling and transportation efficiency in the production process areimproved. Further, an efficient heat generation can be realized by theelectromagnetic wave irradiation. Thus, the amount of alkali can beadjusted to a minimum necessary for the reaction, resulting in greatreduction of the amount of discharged waste alkali.

[0037] It is noted that the present invention is not limited to theabove-described embodiment, and the components, concentrations andamounts of the aqueous alkali to be added can be varied according to thetype, components, properties, etc. of a raw material such asincineration ash. The water amount and the properties of the kneadedmixture, and the frequencies, the irradiation time, etc. of theelectromagnetic waves to be used in the irradiation can also be variedas appropriate.

EXAMPLE 1

[0038] A mixture of coal ash and incineration ash of sludge generated inpaper manufacturing at a ratio of 1:2-5 was treated under theabove-described conditions using the apparatus for producing zeoliteshown in FIG. 1. The conversion rate to Ca-type artificial zeolite wasapproximately 90% when the ratio was in the range of 1:2-3. It waspossible to produce the Ca-type artificial zeolite with high efficiencyby the electromagnetic wave irradiation for the duration of 3 to 5minutes by accelerating the formation of zeolite nuclei through adding10 to 20 percent by weight of glass powder to the incineration ash ofsludge generated in paper manufacturing.

EXAMPLE 2

[0039] Incineration ash from city garbage (RDF incineration ash) wastreated using the apparatus for producing zeolite shown in FIG. 1. Itwas possible to convert the incineration ash to zeolite in one half toone third of the electromagnetic wave irradiation time compared with thecase of treating coal ash.

EXAMPLE 3

[0040] When treating a raw material having a different Si/Al ratio, suchas incineration ash, etc., the components of the artificial zeoliteformed can be controlled by adjusting the ratio of Ca, Na, etc. whichare the components of the aqueous alkali to be added from the alkalistorage tank 3, or by controlling the electromagnetic wave irradiationtime.

[0041] Next, the method of manufacturing artificial zeolite according tothe present embodiment was compared with the method of manufacturingartificial zeolite by means of the conventional hot aqueous alkalinesolution. In the method of the present embodiment, it was possible toreduce the pollution load to 5 kg per one ton of artificial zeolite fromthe conventional 100 kg and to reduce the energy consumption (heavyoil-converted) to 0.05 kl per one ton of artificial zeolite from 0.5 klwhich was necessary in the conventional method. Furthermore, it waspossible to reduce the production cost per one ton of artificial zeoliteto about {fraction (1/3.5)} to ⅕ of the conventional cost.

[0042] Industrial Applicability

[0043] The present invention can be utilized as an efficient technologyfor producing zeolite using incineration ash or a composition containingaluminosilicate, including natural zeolite, as a raw material.

1. A method of producing zeolite comprising: adding an aqueous alkalinesolution to incineration ash or a composition containing aluminosilicateto form a mixture in the form of slurry or mud; heating said mixture;and directly irradiating said mixture with electromagnetic waves havingfrequencies ranging from 300 MHz to 30 GHz, while continuously movingsaid mixture, thereby forming the zeolite.
 2. The method of producingzeolite according to claim 1, wherein said composition is naturalzeolite or zeolite which has not been converted into phillipsite.
 3. Anapparatus for producing zeolite comprising: kneading means for adding anaqueous alkaline solution to incineration ash or a compositioncontaining aluminosilicate to form a mixture and for kneading themixture; heating means for heating the mixture kneaded by said kneadingmeans; electromagnetic wave irradiation means for irradiating saidheated mixture with electromagnetic waves to form zeolite; cleaningmeans for cleaning said zeolite formed by the electromagnetic waveirradiation; and drying means for drying the cleaned zeolite.